1. Field of the Invention
This invention relates to a shell-and-tube type reactor provided with reaction tubes not supported by a donut type baffle plate, a method for the production of (meth)acrylic acid or (meth)acrolein using the reactor; a shell-and-tube type reactor furnished with a plurality of built-in reaction tubes and provided with a baffle plate capable of varying the moving direction of a heating medium introduced into the shell thereof, and a method for the production of (meth)acrylic acid and/or (meth)acrolein using the reactor.
2. Description of the Related Art
The reaction of catalytic gas phase oxidation using a shell-and-tube type reactor is a means generally used for the purpose of efficiently removing the heat generated by the reaction. By the use of shell-and-tube type reactors provided in the shell of the reactor with a plurality of built-in reaction tubes, the raw material gas for the reaction is supplied to the reaction tubes packed with a catalyst to effect the reaction of catalytic gas phase oxidation and the heating medium capable of removing the reaction heat is circulated in the shell thereof to remove the generated heat of reaction.
The reaction of catalytic gas phase oxidation using the shell-and-tube type reactor tends to give rise to a hot spot on the raw material inlet side and poses problems such as deteriorating the catalyst by an excessive exothermic reaction and degrading selectivity to the subject product.
U.S. Pat. No. 3,871,445, for example, discloses a shell-and-tube type reactor provided with a circulation device for a heating medium and further furnished in the shell with baffle plates, in order to solve these problems. It has a mention that, owing to the presence of such baffle plates, the velocity of lateral flow within one area is retained substantially constant and the heat transfer within the area is then fixed. To be specific, the reactor illustrated in the paper has built therein upright reaction tubes arranged in an annular pattern, has the upper and lower ends of the reaction tubes fitted as tightly sealed to the tube sheets, and has a plurality of donut type and disc type baffle plates horizontally and alternately spaced and attached laterally to the reaction tubes so as to form passage sections centrally and externally. The shell is provided at the center thereof with a tie rod and spacer to fix the disc type baffle plates.
The conventional shell-and-tube type reactor which has donut type and disc type baffle plates built therein is schematically illustrated in FIG. 1. Generally, at the center of a shell 1, a tie rod and spacer 7 are disposed to connect the disc type baffle plate 3. The donut type plates 2 are connected through another tie rod and spacer. Reaction tubes 4 are disposed through holes formed in the baffle plates and built in the shell 1. A heating medium 10 is introduced via an annular conduit 11a into the shell 1, for example, using an axial-flow pump not shown. The heating medium 10 so introduced is moved in the shell 1 while changing the flow direction by the donut type baffle plate 2 and disc type baffle plate 3. The transfer of the heating medium 10 is intended to remove the reaction heat from the reaction tubes, and the baffle plates are required for the purpose of securing a passage for the heating medium 10 and enabling the reaction tubes to be uniformly removed of heat. In this case, the reaction tubes 4 are fully supported by the donut type baffle plate 2 without fail. If they are not fully supported, the central hole of the donut type baffle plate 2 is suffered to impart a vertical flow to the heating medium 10 and then the reaction tubes 4 are prevented from sufficiently removing the heat uniformly. The prominence of lateral transfer of the heating medium forces an additional pressure drop of heating medium and calls for an unduly large energy for the power.
The heating medium introduced into the shell is expelled out of the shell after it has been served for the purpose of removing the reaction heat from the tubes, then cooled by a heat exchanger etc, and circulated to the shell to reuse therein. U.S. Pat. No. 5,821,390, for example, discloses a method for effecting catalytic gas phase oxidation of propene into acrolein while maintaining specific selectivity and conversion using a shell-and-tube type reactor, introducing a heating medium in co-current flow, utilizing baffle plates disposed in the reactor, and adjusting the flow rate of the heating medium so that the temperature rise of the heating medium in the reactor falls in the range of 2-10xc2x0 C. This official gazette discloses that the catalytic gas phase oxidation of propene into acrolein is attained using a catalytically active complex metal oxide warmed in the shell-and-tube reactor while reducing the hot spot temperature.
The heat yield is calculated by the balance between the amount of heat generated by the reaction and the amount of heat consumed by cooling. Even when the heating medium is introduced into the shell for the purpose of removing the reaction heat, the failure of removal of the reaction heat uniformly throughout the whole of reaction tubes undeniably entails the possibility that the reaction tubes will suffer an undue temperature rise, increase side reactions, lower the yield of reaction, accelerate deterioration of the catalyst, and induce a run-away reaction. It is clear from the example cited in U.S. Pat. No. 5,821,390 that under the conditions which fix the quantity of heat to be generated, the pump power required to limit the rise of temperature of the heating medium to 1xc2x0 C. is completely identical even if the heating medium is passed in counter or co-current flow within the shell. As a result, the desirability of developing an efficient means capable of uniformly reducing the hot spot temperature in each of the reaction tubes has been finding growing recognition.
Further, there is a time when the heating medium is introduced into the shell, a gas is entrained to introduce into the shell. Since the heating medium receives a large temperature variation as by being heated in consequence of the removal of the reaction heat from the reaction tubes and being subsequently cooled, it tends to include a gas therein with expansion and contraction and this gas eventually collects in the shell. Generally, when the heating medium is introduced into the shell at the start of use of the reactor, an air vent is opened to facilitate the introduction of the heating medium. The air vent is normally kept in a closed state while the reactor is in use. Hence, the gas forms a pool in the upper part of the shell. Since the heating medium is absent from the pool of this gas, the relevant part of the reactor cannot be sufficiently removed in heat. There are times when the reaction tubes may be corroded by the gas.
Thus, the conventional shell-and-tube type reactor relies on the disposition of baffle plates and the cyclic use of the heating medium at a specific flow rate to remove the reaction heat from reaction tubes. This heat removal from the reaction tubes is not called sufficient. When the desired product is manufactured on a commercial scale using this shell-and-tube type reactor, the harmonization between the yield of the product and the power to be consumed constitutes itself an important issue. In particular, an increase in the amount of the heating medium circulated for the purpose of efficiently removing the heat using the shell-and-tube type reactor brings the disadvantage of eventually increasing the power energy for circulating the heating medium. An attempt to enlarge the heat transfer area by decreasing the tube diameter increases the number of reaction tubes and the cost of the reaction apparatus.
Consequently, the development of a reactor capable of uniformly removing reaction heats, reducing hot spot temperatures, maintaining or enhancing the selectivity of the desired product, and decreasing the power energy has been desired.
We have investigated the movement of a heating medium in the reactor and have then discovered that when reaction tubes are disposed on inner sides of donut type baffle plates, the reactor can be miniaturized and the desired product can be obtained in the same yield as in the conventional reactor. This invention has been achieved as a result.
An object of this invention is to provide a reactor for the gas phase oxidation.
Another object of this invention is to provide a method for the production of (meth)acrylic acid and/or (meth)acrolein using the reactor mentioned above.
Further object of this invention is to provide uses for the reactor mentioned above.
The object of this invention is accomplished by a shell-and-tube type reactor provided with a cylindrical shell having disposed on the outer periphery thereof a plurality of annular conduits for guiding a heating medium in or out in the radial direction and having a raw material inlet and product outlet; a circulation device for mutually connecting the plurality of annular conduits; lots of reaction tubes kept by a plurality of tube sheets; and donut type and disc type baffle plates disposed in the longitudinal direction of the tubes and adapted to vary the direction of the heating medium introduced into the reactor shell; and characterized in that the reaction tubes are kept at center distances 1.2-1.4 times the outside diameter thereof; the shell has at the center thereof an empty space devoid of arrangement of the reaction tubes; and the donut type baffle plates avoid supporting part of the reaction tubes.
The object of this invention is further accomplished by a method for the production of (meth)acrylic acid and/or (meth)acrolein using the reactor mentioned above.
The object of this invention is also accomplished by a method for using the reactor mentioned above for the production of (meth)acrylic acid and/or (meth)acrolein.
According to this invention, by disposing such reaction tubes as are not supported by the areas of donut type baffle plates, it is possible to decrease the electric power of a pump. Moreover, this decrease of the electric power is attained without varying the selectivity and yield of the desired product.
The present reactor is particularly suitable for the production of (meth)acrylic acid and/or (meth)acrolein because the use of this reactor can repress the deviation of the temperature distribution of heating medium.
The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments.